I have a lot of respect for the folks at the Greater London Assembly, especially those who worked to get the Train Prediction API exposed and available.
Many people have seen Matthew Somerville‘s Live Map of Underground Trains which was whipped up in a frighteningly short time.
I’m working on a Rails interface to the Train Prediction API, with an ‘advanced’ mode for those who grok the tube. It’s a little rusty, and not even beta-quality, but it’s available for you to play with if you so wish.
Here’s hoping that particular box stands up to the load